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Cardio & Bodybuilding - Good for Muscle Growth?

This article has been featured in Australian IronMan Magazine, Issue 16-4 p94-96.

Among the bodybuilding community, cardiovascular exercise is often viewed as the "unnecessary evil". After all, you don't need to perform any cardio in order to induce hypertrophy. Cardio also isn't a prerequisite to metabolising fat tissue. Some proclaim that cardio will necessarily inhibit muscle synthesis.

However, this narrow minded approach to training can significantly hamper your progress toward your mass building goals. Cardiovascular exercise carries a range of benefits, both physiologically and psychologically. These benefits include fat loss and fitness, but also extend far beyond these area's to hypertrophy, muscular performance, mental strength and general health. In actual fact, cardio work can directly aid you in your weight lifting endeavours.

Not any form of cardiovascular exercise will carry all of these benefits. I'm not talking about a leisurely one hour jog. I am however referring to a highly advanced form of cardio, High Intensity Interval Training (or HIIT).

HIIT Cardio

HIIT is a specific format of cardio typically lasting 10-20 minutes. It incorporates intermittent breaks to allow the body to recuperate between high intensity working periods. These breaks are known as periods of "active recovery" where you are able to regain your breath and lower your heart rate slightly. With these small recovery periods, the intensity can therefore be significantly enhanced throughout the sprint sessions. Quite simply, an increased intensity can lead to increased results through a higher level of overload.

HIIT certainly isn't for the faint hearted because it does require a significant amount of physical and mental strength. If you invest the time and effort, you will reap the (very) significant rewards. Let's discuss precisely why HIIT cardio is NOT the enemy.

Hypertrophy & Muscle Performance

Significant muscle gain is most commonly induced as a result of overload acquired through resistance training. However it has been demonstrated that high intensity cardio can directly induce an anabolic response to stimulate muscle synthesis. This has been demonstrated in a number of studies where low intensity cardio groups have tended to lose muscle mass, whilst high intensity cardio groups have actually maintained or gained lean body mass.1,2,3

Interestingly, high intensity cardio can also improve a muscles ability to perform more effectively under other intense conditions, such as resistance training. Here's the science:

The "burn" that you feel from exercising is a result of the accumulation of H+ ions. Some refer to this burning sensation as "lactic acid". This is a result of the breakdown of adenosine triphosphate (ATP) into adenosine diphosphate (ADP) that occurs when force is generated from skeletal muscle tissue. As these H+ ions accumulate, the muscular environment becomes more acidic, known as acidosis. Within a muscle, acidosis results in:

  • The inhibition of the muscles ability to contract by interacting with the calcium ions present
  • The slowing of the ATP breakdown

In other words, a highly acidic (or low pH) environment means that you will reach muscular failure.

Enter lactate threshold.

The lactate threshold refers to a muscle's buffering system, or it's ability to prevent the accumulation of H+ ions. As a muscle's lactate threshold improves, the buffering system becomes more effective at reducing acidosis within that particular muscle fibre. So in summary, the higher your lactate threshold, the more efficient your muscle is at preventing a significant decrease in pH that results in muscular failure. This effectively means that by performing HIIT cardio using a particular set of muscles, you can improve their performances in the weights room. Better performance means more overload and thus more growth.


High intensity interval training has a profound positive influence on your level of fitness. Fitness can take on a number of definitions, but for the purposes of this bodybuilding discussion, we will refer to anaerobic capacity, or where oxygen is not utilised to generate force. This is most prevalent in short, high intensity bouts of exercise, such as during HIIT.

One particular study conducted in 1996 by Tabata et al considered a group of participants that performed HIIT. They exercised at an intensity of 170% of VO2max for 20 seconds, with a 10 second rest, repeated for a total of 4 minutes. At the conclusion of the study, these participants demonstrated a 28% increase in their anaerobic capacity.4

High intensity weight training also recruits the same energy systems (primarily the phosphate and lactate systems). Considering this, HIIT cardio will therefore have a direct positive influence on your resistance training.

General Health

When striving to achieve hypertrophy or strength goals, general health can be easily overlooked. But after further consideration, this seems to be quite counterintuitive. After all, if you are in a healthier state, your body is going to be able to perform at an optimal level. Of particular direct relevance to bodybuilding, the following systems are very important to your mass building goals:

  • Cardiovascular system, for circulation, nutrient transport etc.
  • Endocrine system, for hormone production
  • Muscular system, for force generation by the body
  • Nervous system, the "master" controlling and communications system
  • Respiratory system, for the body's oxygen supply

From their functions, you can infer how each of these systems will affect your results in the weights room. Cardiovascular training is an integral part to your general health, in conjunction with appropriate recovery, nutrition, resistance training, lifestyle etc.

Long-term considerations must also be made with resistance training. After all, bodybuilding is not an overnight affair and requires years of dedication. It makes even more sense in this regard to consider your general health and wellbeing in order to ensure the longevity in your ability to participate in high intensity training. Cardiovascular exercise plays an important role in this by reducing the risk of many diseases, including heart disease, high blood pressure, type 2 diabetes, stroke and colon cancer.5

Mental Strength & Focus

Until you have performed a HIIT cardio and pushed yourself maximally, it is unlikely that you will be able to appreciate the mental strength and focus required. From the very first sprint, you need to invest 100% of your physical and mental energy to obtain that new personal best. Half way through the session, you hit that "half-way bump" where your mind begins to tell you to slow down and save some energy for the finish. By the final few minutes, you are utterly exhausted, but in order to obtain that new personal best, you need to push harder than ever before.

No matter how many times you perform HIIT cardio, you can always increase the intensity next time. For this reason, HIIT cardio is just as much (if not more) a mental battle, as it is a physical battle. By consistently striving to always improve your performance, you develop a strong sense of discipline, focus, humility, confidence and self-awareness. These ever-developing assets transcend into all area's of life, whether that be social, work, family, or even just in the weights room.

Fat Loss

It is widely accepted that HIIT is very effective at oxidising fat. The high intensity interval nature of this cardio develops a significant EPOC (Excess Post-exercise Oxygen Consumption), or "residual thermogenesis" following the workout. Effectively this means that HIIT can turn your body into a fat burning machine after the conclusion of the workout.

Whilst there are a myriad of studies that evidence the above, there is one conducted in 1996 that is particularly memorable. Tremblay et al. compared two cardio groups; one performing endurance cardio and another performing HIIT. The HIIT group demonstrated an amazing nine times more fat loss than the endurance group. The conclusion was that "[metabolic adaptations resulting from HIIT] may lead to a better lipid utilization in the post-exercise state and thus contribute to a greater energy and lipid deficit". 6

As you can see, HIIT cardio is NOT the enemy when trying to build muscle. The real enemy is the inability to develop a symbiotic relationship between cardiovascular training, resistance training, nutrition and recovery in order to maximise your results.


  1. Grediagin A, et al. Exercise intensity does not effect body composition change in untrained, moderately overfat women. J Am Diet Assoc. 1995 Jun;95(6):661-5.
  2. Mougios V, et al. Does the intensity of an exercise programme modulate body composition changes? Int J Sports Med. 2006 Mar;27(3):178-81.
  3. Okura T, et al. Effects of exercise intensity on physical fitness and risk factors for coronary heart disease. Obes Res. 2003 Sep;11(9):1131-9.
  4. Tabata I, et al. Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and ?VO2max Medicine & Science in Sports & Exercise:Volume 28(10)October 1996pp 1327-1330
  5. U.S. Department of Health and Human Services. Physical Activity and Health: A Report of the Surgeon General. Atlanta, GA: Centers for Disease Control and Prevention (CDC), National Center for Chronic Disease Prevention and Health Promotion, 1996.
  6. Tremblay, et al, Metabolism (1994) Volume 43, pp.814-818
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